Collaborative projects in the environmental health sciences includes those projects in which the mass spectrometry work-group collaborates with other groups, both within and without the institute to solve problems of mutual interest. The major focuses of these projects are 1) the structure determination of biological compounds of unknown structure, 2) identification and/or confirmation of biological pathways and 3) development of strategies for the structure determination of biologically important compounds. Major projects currently under investigation include; 1) the identification of the presence of leukotriene B4 in airway epithelium tissues; 2) the structure determination of hepatopoietin B, a low molecular weight compound in serum that stimulates hepatocyte DNA synthesis and is hypothesized to be the prototype molecule mimicked by xenobiotic compounds, such as phenobarbital, that cause hepatocyte hypertrophy and proliferation; 3) the structure determination of the small peptides expressed by cells infected with flu virus that cause the cell to be recognized by T-cells as being infected (a model of HIV infection) and; 4) the development of combined LC/EPR/MS techniques for the identification of spin-trapped free radicals. This latter projects involves the structure determination of chemically produced free-radicals and of free-radicals produced as intermediates in enzymatic processes in biological systems.